For maximum user comfort in terms of cooling the areas where the user's body contacts the seat, active cooling systems are used, i.e. systems comprising a fan underneath the seat portion to blow air from the vehicle interior into the seat portion or in the opposite direction to increase heat exchange and so withdraw heat.
Known active systems are unsatisfactory on account of the not always positive sensation experienced by the user.
That is, on first sitting down on the seat, the user tends to experience discomfort, which is directly proportional to the initial degree of heat exchange between the user's body and the seat. Because of the sudden withdrawal of a large amount of heat by the fan, the user experiences a chilling feeling when sitting down on the seat, especially if accompanied by severe perspiration.
To eliminate this drawback and so reduce initial heat exchange, a “passive” solution, i.e. with no fan, is preferable, and in which the initial user-seat sensation is substantially determined by the characteristics of the seat upholstery.
In this connection, DE2136947A1 describes a seat portion with spaced tubular bodies embedded in the padding. The tubular bodies are made of flexible material and define respective chambers, which communicate with the outside at the top end through upholstery permeable to air, and at the bottom end through respective flap valves fitted to a bottom wall; and the tubular bodies are surrounded by respective coil springs also embedded in the padding.
When the vehicle is moving, the valves are opened and closed cyclically by the weight of the user sitting on the seat, and by vibration from the road. That is, vibration causes a vertical up-down movement of the user, in which downward movement presses on the padding and deforms the tubular bodies and the springs, thus compressing the air in the chambers, and upward movement reduces the pressure and allows the tubular bodies and springs to expand, thus reducing the pressure inside the chambers. During compression, the valves close, and the air in the chambers flows out through the upholstery; and, during decompression, the valves open, and more air is sucked into the chambers from underneath through the valves.
In other words, normal use of the seat portion as the vehicle is moving produces an automatic or natural pumping effect to circulate air through the seat portion and so cool the areas where the user's body contacts the seat portion.
Though effective operationwise, the above solution has the drawback of comprising a large number of parts.
In order to reduce the number of parts, it is theoretically possible to provide a single valve for all the chambers, by putting the bottom ends of the chambers in communication with each other. However, in this case, if the average of air compression and air decompression in the ensemble of the chambers is constant, the valve does not open and, therefore, there is not air recirculation.